To the Editor:
In their article “Sleep Patterns in Late Pregnancy and Risk of Preterm Birth and Fetal Growth Restriction,” Micheli et al1 reported a 2-fold increase in the risk of fetal growth restriction in pregnant women with severe snoring in the last trimester of pregnancy. In the discussion section, the authors stated that their results were in accordance with the findings of Bourjeily et al.2 However, this statement is not entirely correct. Although Bourjeily's study2 showed an association between snoring and preterm birth (which was likely mediated by preeclampsia), it did not show a significant association between sleep-disordered breathing and growth restriction (odds ratio = 1.9 [95% confidence interval = 0.8–4.3]). The discrepancy may be due to the difference in the definition of growth restriction—Micheli at al corrected for familial characteristics (maternal and paternal height and age, as well as prepregnancy maternal weight), whereas Bourjeily et al2 did not—or to the difference in the sample size of snorers (n = 48 in Micheli's study vs. n = 333 in Bourjeily's study).
Micheli et al also referred to the study by Sahin et al3 as another study supporting their findings. Sahin's study's primary goal was evaluation of clinical tools in predicting obstructive sleep apnea and fetal heart rate variability in response to apnea, and not growth restriction. Their study found only 4 women with obstructive sleep apnea who had other comorbidities. These data are hardly supportive of this hypothesis.
Despite body mass indices (BMIs) that are likely comparable with other studies performed in pregnant women,2 the incidence of severe snoring in Micheli's study1 is unexpectedly low—4% versus 14% to 45% in other studies4 of women with similar age and race characteristics. This rate of snoring in Micheli's study1 is close to the rate of snoring in nonpregnant women. It would be helpful to the reader if the authors mentioned mean BMI in their entire sample and offered an explanation for their low rates of snoring.
The question of the effect of snoring on growth restriction remains a controversial one, with some studies showing a significant effect and others failing to show such an effect. These discrepancies may be related to differences in sample size, lack of adjustment for confounders, variation in outcome definition, possible difficulties with appropriate dating of pregnancies, and lack of serial fetal growth assessments.
Department of Medicine
Staten Island University Hospital
Staten Island, NY
Department of Medicine
The Miriam Hospital
1. Micheli K, Komninos I, Bagkeris E, et al.. Sleep patterns in late pregnancy and risk of preterm birth and fetal growth restriction. Epidemiology. 2011;22:738–744.
2. Bourjeily G, Raker CA, Chalhoub M, Miller MA. Sleep disordered breathing symptoms in pregnancy and adverse pregnancy and fetal outcomes. Eur Respir J. 2010;36:849–855.
3. Sahin FK, Koken G, Cosar E, et al.. Obstructive sleep apnea in pregnancy and fetal outcome. Int J Gynaecol Obstet. 2008;100:141–146.
4. Bourjeily G, Anker G, Mohsenin V. Sleep-disordered breathing in pregnancy. Clin Chest Med. 2011;32:175–189.